Commercially available three-dimensional printers (3D), such as the Projet™ 3D Printers manufactured by 3D Systems of Rock Hill, S.C., use a build material or ink that is jetted through a nozzle as a liquid to form various thermopolymer parts. Other printing systems are also used to build 3D parts from material that is extruded through a nozzle (for example, CubePro 3D Printer manufactured by 3D Systems). In some instances, the build material is solid at ambient temperatures and converts to liquid at elevated extrusion temperatures. Well-known build materials are polyamide, poly(acrylonitrile-butadiene-styrene) (ABS) and polylactic acid (PLA).
Production of a three-dimensional part in a 3D printing system often requires the use of a support material in conjunction with the build material. The support material may be necessary to support overhanging segments or portions which are not directly supported in the final geometry by the build material. The support material may be useful for several other purposes, e.g., to minimize warping from the build material's own load, to produce hollow sections, and/or to enable several moving components in the same part. The support material is also extruded in the same fashion as the build material through a separate nozzle. However, unlike the build material, the support material is subsequently removed after printing to provide the finished three-dimensional part. The support material should be removable without damaging the printed build material.
Removal of the support material has been administered through several processes, including heating the support material to a temperature above its melting point in conjunction with the use of a suitable organic carrier to sufficiently remove the support material from the build material. In some cases, the organic carrier deposits an undesirable oily residue on the completed three-dimensional part. Furthermore, the use of elevated temperatures, in addition to a suitable organic carrier, in some situations can compromise the mechanical integrity of the finished three-dimensional part resulting in part deformation or failure.
To solve this problem, U.S. Pat. No. 5,503,785 suggests depositing a release material as a thin coating between the build material and the support material. The release material is a hydrocarbon wax or a water-soluble wax, acrylates, polyethylene oxide, glycol-based polymers, polyvinyl pyrrolidone-based polymers, methyl vinyl ethers, maleic acid-based polymers, polyoxazolidone-based polymers, Polyquarternium II or conventional mold release materials, such as fluorochemicals, silicones, paraffins or polyethylenes. Depending on the type of release layer, it may also leave an undesirable oily residue on the completed three-dimensional part. Moreover, the release layer adds complexity to the three-dimensional printing of the articles.
A well-known support material is High Impact Polystyrene (HIPS). After the 3D printing, HIPS can be dissolved in limonene to remove HIPS from the printed build material. Unfortunately, limonene has a low flash point and leaves hazardous toxic wastes.
Another known support material is polylactic acid (PLA). It can be dissolved in a heated sodium hydroxide solution, which is hazardous to handle. Unfortunately, PLA leaves corrosive, hazardous toxic wastes.
U.S. Pat. No. 6,070,107 discloses the use of poly(2-ethyl-2-oxazolidone) as water-soluble rapid prototyping support and mold material. Unfortunately, poly(2-ethyl-2-oxazolidone) is very tacky. Moreover, on thermal decomposition of poly(2-ethyl-2-oxazolidone) toxic fumes are generated, specifically nitrogen oxides and carbon oxide, as disclosed in its Material Safety Data Sheet.
It is well known to use polyvinyl alcohol (PVA) as a support material for ABS. PVA and ABS can be printed simultaneously. After the 3D printing has been completed, the printed article can be submerged in water. The PVA is dissolved in warm water and leaves the ABS portion of the printed article intact. Unfortunately, PVA is quite difficult to print, does not sufficiently adhere to ABS and takes a long time to dissolve. However, some adherence of the support material to the build material is very desirable to provide a good support and minimize warping of the build material.
In view of the deficiencies of support materials in three-dimensional printing, it would be desirable to provide a support material that avoids one or more of the problems of the prior art such as those described above.
A preferred object of the present invention is to provide a support material that is easily removable from the build material after three-dimensional printing of the support material and the build material. Another preferred object of the present invention is to provide a support material that does not leave substantially toxic or corrosive waste upon removal of the support material (e.g., is easily removed in neutral pH water). Yet another preferred object of the present invention is to provide a support material that has a reasonably good adhesion to the build material. To facilitate handling, yet another preferred object of the present invention is to provide a support material that has a low level of surface tackiness.